Should Filter Paper Be Wet? What Impact Does Dry Filter Paper Have on Pour-Over Coffee? Why Use Twice as Much Water for Blooming?

Last month, FrontStreet Coffee shared the differences between wetting and not wetting filter paper. Many coffee enthusiasts who enjoy delving into details noticed a key point mentioned in the article: unwetted filter paper absorbs coffee liquid during the brewing process. However, the brief mention in the article obviously didn't answer their questions, so they reached out to FrontStreet Coffee in the background with their queries: Do different filter papers absorb the same amount of liquid? What impact would missing this portion of coffee liquid have on the overall taste of the coffee?

Experimental Design

Excellent! Since you've asked with sincere curiosity, FrontStreet Coffee will conduct an experiment to answer your questions: In this experiment, we will use two types of drippers - the V60 and the Origami. One uses cone-shaped filter paper, the other uses flat-bottom filter paper, each forming a separate group. Let's see what differences exist in liquid volume, concentration, and taste between coffee brewed with wetted versus unwetted filter paper! (The filter paper used doesn't have any other undesirable properties such as off-flavors)

Brewing Experiment

The coffee beans used in this brewing experiment are Finca Limonera - Ombligo, with cupping notes of blackcurrant, blueberry, and sweet orange. We used 15g of coffee grounds with a 1:15 coffee-to-water ratio. The water temperature was 92°C, ground to 9.5 on the EK43 (fine sugar consistency). The brewing method was three-pour. Now, let's begin our brewing! (Brewing process omitted)

Experimental Results

Since both dripper sets have ribbing, the brewing time between wetted and unwetted filter paper differed by about 7 seconds, with the wetted filter paper taking slightly longer to finish brewing (V60 at 2 minutes 6 seconds, Origami at 2 minutes 12 seconds). Next, let's weigh the liquid~ FrontStreet Coffee precisely poured 225ml of hot water, and ultimately, whether using the cone-shaped filter paper in the V60 or the flat-bottom filter paper in the Origami, both coffees brewed with wetted filter paper yielded approximately 190ml of liquid, while both coffees brewed with unwetted filter paper yielded approximately 184ml.

(V60 group)

(Origami group)

This means that after accounting for the 30ml of hot water absorbed by the coffee grounds, the filter paper only absorbs about 5ml of coffee liquid. So what impact would this 5ml have on coffee concentration and taste? Next, please welcome our concentration tester and FrontStreet Coffee's testing personnel to conduct separate evaluations!

(V60 group)

(Origami group)

Analysis and Conclusion

From the parameters displayed on the concentration tester, it can be seen that excluding differences caused by brewing technique, there isn't significant difference between the two. Our testing personnel also indicated that the taste of all four coffees showed almost no difference (in comparisons within their respective groups). Therefore, we can conclude that the missing coffee liquid absorbed by the filter paper doesn't significantly impact the overall coffee. This is also related to the coffee liquid absorbed by the filter paper. Because when we don't wet the filter paper, the filter paper absorbs the first coffee liquid it encounters to saturate itself. And this first portion of coffee liquid typically has the lowest concentration, so it doesn't affect the overall coffee.

Why is the first coffee liquid to contact the filter paper the lowest in concentration? We know that the purpose of blooming is to pre-release carbon dioxide from the coffee grounds, allowing subsequent hot water to better extract the aromatic substances from the coffee grounds. The hot water poured during blooming contacts coffee grounds that haven't been degassed, so they cannot extract aromatic substances from the coffee as effectively as subsequent pours of hot water. This results in insufficient extraction rate, preventing them from achieving adequate coffee concentration.

Therefore, we try to use the minimum amount of water to complete the blooming step, reducing the "waste" of hot water. Coincidentally, dry coffee grounds themselves absorb water, so we perform blooming with the amount of water that the coffee grounds can absorb (twice the weight of the grounds), which minimizes "waste" as much as possible, although not all of this hot water will be absorbed. The liquid that unwetted filter paper first encounters is precisely this unabsorbed portion. Because it passes through coffee grounds that haven't been fully degassed, it doesn't carry much coffee substance. Therefore, even missing this portion of coffee liquid won't significantly impact the overall taste (in terms of flavor, there's an effect, but truly minimal)~

As for other impacts of wetted versus unwetted filter paper, FrontStreet Coffee has actually explained them in detail in the previous article, so we won't repeat them here~

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473